FIG. 1 is a simplified cross-sectional schematic drawing of a cooling fan. Ring 3, also shown in FIG. 2, supports an array of radial stator vanes 6, shown in both Figures. Ring 3 is anchored to an external support (not shown). Stator vanes 6 in FIG. 1 support an inner ring 9, which is also shown in FIG. 2. It should be understood that the structure identified as ring 9 does not have to take the form of a ring or a complete cylindrical 360° body of revolution. Inner ring 9 in FIG. 1 supports a motor, diagrammatically indicated as motor 12, which may be an electric or hydraulic motor. Motor 12 drives fan blades 15, which are supported by bearings 18.
Ideally, inner ring 9 acts as a perfectly rigid support for the motor 12. However, in practice, this ideal is not attained, and the motor 12 and the inner ring 9 can move in an axial or tangential fashion, which is not desired.
Further, a given fan system will possess certain natural or resonant frequencies. If an excitation occurs at these frequencies, as when the fan is attached to an automotive engine and the engine vibrates at such frequencies, the fan system will sympathetically vibrate at these frequencies. In general, such sympathetic vibration is not desired. A sympathetic vibration of the fan system can be the source of objectionable noise or vibration that can be noticed within the passenger compartment.